1. Field of the Invention
The invention relates to a radio station for transmitting signals. The radio station includes a modulator modulating the signal to be transmitted, a power amplifier amplifying the modulated signals, a summing device subtracting a test signal of the power amplifier for a reference signal to generate a control signal and an antenna for transmitting and receiving the signals.
In GSM (Global System for Mobile Communications), antennas in mobile phones are optimized for a predefined resonance frequency and a given frequency bandwidth.
2. Summary of the Invention
It is accordingly an object of the invention to provide a radio station for transmitting signals that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and, in which, a change of a resonance frequency of the antenna is minimized by adjusting an impedance being in parallel or in series with the antenna, so that the resonance frequency deviates only slightly from its predefined value due to changes in the surroundings of the antenna. In this way, the reflection characterized by the voltage standing wave ratio (VSWR) is also minimized, so that most of the power is transmitted. This has the advantage to saving battery life and it also increases the life of other electrical components in the mobile phone that do not need a large amount of reflected power.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a radio station for transmitting signals. The radio station includes a modulator modulating a signal to be transmitted. A power amplifier connected to the modulator amplifies the modulated signal and producing an output power and a test signal. A summing device connected to the power amplifier subtracts the test signal of the power amplifier from a reference signal to generate a control signal. An antenna can transmit and receive the signals. Impedance with a variable reactance is switched between the antenna and the power amplifier. An analog-to-digital converter converts the control signal to a digital signal. A processor uses the digital signal to change the variable reactance of the impedance.
In accordance with a further feature of the invention, a processor calculates an optimum value for the impedance being switched to the antenna according to a measurement of the output power of a power amplifier in a transmitter of the mobile phone. Thereby, the output power is maximized.
Furthermore, it is an advantage that the processor stores the calculated values for each measured value, so that later, when again the measured value is measured, the processor simply takes the previously calculated value for the impedance in order to save processing time.
In accordance with a further feature of the invention, a directional coupler for transfers a part of the output power to a power detector, so that the power detector converts the part of the output power to a test voltage. The test voltage is used for adjusting a power amplifier and the variable reactance.
Moreover, it is an advantage to use a current of a last stage of the power amplifier to characterize the output power of the power amplifier for adjusting the power amplifier and the impedance. This is an easy solution and requires less circuit elements.
In accordance with a further feature of the invention, a voltage of the last stage of the power amplifier characterizes the output power of the power amplifier. This is an easy and exact solution to characterize the output power.
In accordance with a further feature of the invention, a plurality of capacitors and conductors adjust by switching some of those capacitors and inductors for the adjustment of the variable reactance.
Alternatively, in accordance with a further feature of the invention, the capacitors and inductors for the variable reactance can be changed individually. In this way, the number of necessary circuit elements for the impedance is reduced. This reduction lowers the cost of manufacturing.
Apart from this, a further feature of the invention uses different types of microstrip lines to provide the capacitance and inductance of the impedance. This leads to an easy, cheap, and straightforward implementation of the impedance.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a radio station for transmitting signals, the invention is nevertheless not intended to be limited to the details shown, because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.